Protecting and insulating covering for furnace support members



J. S. BARKER June 24, 1969 PROTECTING AND INSULATING COVERING FOR FURNACE SUPPORT MEMBERS Sheet Filed Jan. 18. 1968 INVENTOR JOHN s BARKER ATTORNEYS June 6 J. s. BARKER 3,45l,661

raomcmue AND INSULATING cov ame FOR FURNACE suprem urim-:sms

Filed Jan. 18. 1968 Sheet g o`f 3 INVENTOR F/G 5 JOHN s. BARKER ATTORNEYS June 1969 1. s. BARKER 1,661

U ING COVERING FOR FURNACE SU 0 PROTECTING AND INS LAT T MBERS Filed Jan. 18, 968 v Sheet 3 of 3 I INVENTOR I JOHN S. BARKER BY Qaj/% ATTORNEYS United States Patent O U.S. Cl. 263-6 16 Claims ABSTRACT OF THE DISCLOSURE An arrangement for protecting and insulating water cooled tubular support members in a furnace of the type used for heating steel ingots after the ingots have been formed into suitable shapes such as billets, blooms or slabs. An inner layer of resiliently deformed insulating material covers the support member. An outer layer of interlocking refractory elements covers the inner layer and (a) holds it in radial compression while (b) the inner layer in turn holds the outer layer in a state of circumferential stress. The refractory elements are designed to permit limited freedom of movement therebetween to accommodate the effects of thermal stresses and vibrational shocks.

BACKGROUND Field of the invention This invention relates to metallurgical furnaces of the type used to reheat previously shaped ingots, wherein the shaped ngots to be treated move along rails, the heat being supplied from burners above and below the rails. In particular, the invention relates to an arrangement for protecting and insulating the water cooled tubular support members such as skid rails, support tubes and the like, which support the weight of the ingots under treatment.

Environment of and problems underly'ng the invention In the preparation of steel, steel ingots are first heated to a uniform temperature and then rolled into various shapes such as bllets, slabs, blooms, etc. The once rolled ingots are then reheated for further rolling. The present invention concerns the furnace in which the shaped ingots are further heated. While this type of furnace may take many different forms, it will be referred to hereinafter, generically, as a slab reheating furnace" and the invention will be discussed with respect to a shaped ingot in the form of a slab.

The slabs move through the furnace on horizontal water cooled pipes known as skid rails which are supported from below by horizontal and vertical water cooled steel support tubes. Because it is essential that the slabs be heated uniformly, burners must be provided both above and below the level of the slabs. However, this necessitates placement of the skid rails and support tubes in the path of the hot oxidizing gases emanating from the lower burner. Thus, the immense weight of the slabs and the high temperature of the gases in the furnace place great demands upon the skid rails and the support tubes.

Clearly, the skid rails and the support tubes must be protected by sufiicient insulating material to minmize the flow of heat from the interior of the furnace to the water cooled tubes. Such heat flow would reduce the Operating efliciency of the furnace for at least two reasons. First, it would draw off otherwise useful furnace heat, and

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second, it would place a greater burden on the system which cools and Supplies water to the water cooled tubular support members.

Conditions within the furnace place strong demands on the Construction and design of the protecting and insulating material. High temperatures, large temperature gradents, extreme mechanical shocks (caused by irregular or bouncing movement of the slabs along the skid rails) and the piercing effect of falling pieces of slag require that the protecting and insulating material (1) must be very thick and/or (2) must be either constituted by or at least protected by strong refractory material.

It might be relatively simple to provide an adequate protecting and insulating layer on the skid rails and support tubes if no restrictions were placed upon the overall diameter of the protecting and insulating layer. However, as noted above, these tubular support members are located in the path of the hot gases between the lower burner and the slabs, as a result of which the tubular support members tend to "shield" or shadow the bottoms of the slabs -from the heat generated by the lower burner. The effect of shadowing is to rob the lower portion of the furnace of valuable combustion space and thereby produce an uneven temperature distribution through the slab. As one manifestation of this problem, the temperature of the slabs is generally lower along the lines where the skid rails physically contact, and thereby heavily shadow the bottoms of the slabs.

As noted above, however, it is essential that the slab be heated uniformly. Consequently, towards eliminating the elfect of shadowing, the overall diameter of the skid rails and the support tubes, including the inner and outer protecting and insulating layers, should be kept as small as possible.

Finally, the solution to the various problems outlined above must be an economical one. To be economical, an insulating and protecting arrangement for a tubular support member must be durable (so that replacement is required only infrequently), it should maintain its structural integrity between replacements (so that furnace eificiency is not reduced for long perods between replacements) and it should be capable of easy and rapid replacement (thereby minimizing furnace shut down time).

Description of the prior art The task of designing a truly improved skid rail and support tube protecting and insulating arrangement is complicated by the fact that the obvious solution to one problem tends to be contrary to the obvious" solution to another problem. For example, good heat retention in the furnace requires a thick insulation but this only increases the detrimental elfect of shadowing. The prior art to date is composed mainly of compromise solutions which have solved some of the problems either to the detriment of or while ignoring the other problems.

An early attempt to provide a suitable heat barrier between the furnace and the water cooled tubes included surrounding the tube with a layer formed by a plurality of large, rigd sections formed of a refractory material, leaving a space between the tube and the inner surface of the refractory layer. An example of this arrangement is shown in the Schmidt U.S. Patent No. 2,436,452. However, this arrangement requires that the large sections (1) be mounted on studs or other mounting members in direct heat transfer relationship with the tube and (2) be rigidly held to each other. Because of the tight, rigid fit between the sections the refractory layer cannot yield so as to withstand the instense vibrational shocks caused by movement of the slabs; and because of the discrepancy in heat flow characteristics between the studs and the refractory material, large thermal gradients are established and these &4511561 in turn cause thermal stresses. The efi'ect of the vibrational shocks and the thermal stresses is to cause cracking of the large section. On the other hand, it is not always feasible to eliminate the tight fit between the sections since this would create air spaces between the sections for the flow of heat and gases from the furnace to the water cooled tube. Moreover, because the gases in the furnace are oxidizing in nature, they tend to corrode the tube. Another disadvantage of the large sections is that they are normally held together in a complex arrangement thereby rendering replacement of a single section quite difcult without replacing the entire layer.

In another prior art arrangement the large sections are replaced by a one-piece refractory layer moulded directly onto the tube and help in place by suitable means such as a wire mesh welded to the tube. An example of this arrangement is shown in the U.S. patent to Bloom, 2,693,352. This arrangement does not eliminate the cracks derived from thermal stresses and vibrational shocks. However, it does provide the advantage that at least the pieces are held in place on the tube for a longer period of time by the wire mesh. However, the moulding approach creates at least two additional problems: (1) since the material is moulded directly onto the tube it probably cannot be heated to a temperature above its green strength" to provide maximum st-rength and (2) replacement time for moulding a layer of refractory material would be relatively long thereby increasing shut down time of the furnace.

Still another prior art approach includes arranging a plu-rality of sectional refractory elements partally circumferentially about the water cooled tube, holding the sections in place with mounting elements connected to the tube and with tongue and groove connections between the sections, and placng a layer of ceramic fiber insulating material in the annular space between the refractory layer and the tube. A circnmferential gap is left between the last two elements, and this gap is closed with a refractory mortar. Such an arrangement is shown, for example, in U.S. Patent No. 3,226,01O to Balaz. However, this arrangement would apparently suffer from the same disadvantages as the earlier approaches which employed direct heat flow passages in the form of mounting means between the furnace and the water cooled tube. Moreover, if the refractory elements are held tightly together, it would appear that this arrangement would not accommodate the vibrational shocks caused by movement of the slab along the rails. On the other hand, as noted earlier, if the refractory elements are not held tightly together, additional passages would be provided between the sections for heat loss and for the fiow of Corrosive gases from the furnace to the metal tube. The mortar closure usually lacks durability, and the service life of this arrangement often leaves much to be desired.

SUMMARY OF THE INVENTION The purpose of the present invention is to provide a new and substantially improved arrangement for protecting and insulating tubular support members such as skid rails and support tubes, which arrangement economically and efiiciently satisfies the strong demands placed upon it by the nature of the slab reheating furnace. It should be understood, however, that the invention may also be applicable to other types of furnaces where similar conditions exist.

Basically, the essence of the present invention is the concept of providing an insulating and protecting arrangement comprising an inner layer of resiliently deformable insulating material covered and held in radial compression by, and in turn holding in circumferential stress, an outer layer of flexibly interlocked refractory elements, wherein the arrangement is self-supporting, i.e. it remains in place, without any additional attachng means such as ties, connectors, mortar, studs and the like.

For most tubular support members, such as horizontal and vertical support tubes, the protecting and insulating arrangement can be complete circumferentially and the inner and outer layers are then completely cylindrical and the interlocking joints of the refractory elements of the outer layer are held in circumferential tension.

However, for some members, particularly the skid rails themselves which each have an exposed longitudinal rib on which the slabs slide, the layers cannot be completely circumferential and in such case the layers extend only partly around the skid rail e.g. up to each side of the skid rib, and the interlocking joints of the elements of the outer layer are designed to lock by circumferential abutment in the form of an incomplete circumferential arch and are held in circumferential compression.

The layers may be assembled according to at least the following two methods. First, the preformed mats of insulating material may be placed about the tubular support members after which the nterlocking refractory elements may be placed around the insulating layer and interlocked thereby compressing the refractory layer radially against the resiliently deformable insulating materal. Alternatively, the layer of refractory material may first be preassembled about the support member leaving an interspace between the support member and the assembly of interlocking refractory elements. The fibrous insulating material would then be stufed into the space with sufiicient force to circumferentially stress the layer of refractory elements.

The individual interlocking refractory elements each have a head portion and a tail portion, the two portions being complementary so that the tail will interlock with the head of an adjacent element. The elements, as a whole, are of the same shape in a given assembly. The fit between the head of one element and the tail of the next adjacent element is such as to permit limited treedom of movement of the elements relative to each other to accommodate thermal stresses and vibrational shocks while the elements are still held tightly on the layer of insulating material.

In one embodiment the head and tail are formed as cooperating fianges extending radially (relative to the axis of the support member), one flange extending outwardly and the other flange extending inwardly. In the assembled state the head and tail of adjacent elements would interlock. In another embodiment the head and tail are formed, respectively, as an enlarged projection at one end and as a groove at the other end. In this embodiment the head may include a rclieved portion to provide a space between a portion of the head and the interior of the groove thereby permitting limited freedom of movement between the head and the groove. In this embodiment, the shoulders of the elements (the surfaces adjacent the projecting heads) are shaped to permit the elements to be formed into a circular path about a circular support member.

The widths of the interlocking elements (the dimension taken along a line parallel to the axis of the support member) may all be identical. In this case it would be possible to form the elements on the support member in longitudiral and/or circumferential rows. Alternatively, the widths of the elements may be different in which case one could form only longitudinally extending rows.

It is preferable that the interlocking refractory elements have as few sudden changes in their dimensions as possible, since such changes create points of stress. For this reason, the first mentioned type of interlocking element, having radially extending inner and outer flanges, is preferred to the interlockng element formed with a projection-type head and a groove-type tail.

Thus, it is believed that the present invention efiiciently and economically satisfies the numerous demands placed upon the tubular support member protecting and insulating arrangement by the slab reheat furnace` The continuous,

uninterrupted and self-supporting layers of insulating material and refractory material permit the elimination of mounting studs and the like connected directly to the support members, thereby making possible a more compact arrangement and reducing the effects of shadowing; and the damaging heat flow paths from the furnace to the support members are eliminated thereby reducing a major cause of heat loss and thermal gradients in the refractory layer. Moreover, this arrangement leaves no openings for Corrosive gases to flow from the furnace to the surface of the support members.

The resiliency of the insulating layer together with the limited freedom of movement of the individual nterlocking elements permits the refractory layer to accommodate the vibratonal shocks and thermal stresses. Furthermore, thermal stresses in the refractory elements are minimized by minimizing the thermal gradients across the elements. While there is a large thermal gradient radially through the entire assembly, the gradient occurs primarily across the ceramic fiber insulating material rather than across the refractory elements. The invention thus minimizes the thermal stresses, and adequately accommodates those that remain.

The nature of the interlockng elements renders the arrangement extremely economical. Initial assembly and replacement are both simple and rapid. Consequently, the elements may be assembled with a minimum of skill and with a minimum of fumace shut down time. Finally, a major advantage of the present invention is a greatly increased life spn, thereby reducing the frequency of replacement.

Thus, it can be seen that the advantageous results of the present invention are provided by the new cooperation and interrelationship between a layer of resiliently deformable insulating material and a specifically designed arrangement of interlockng refractory elements.

Thus, it is an object of this invention to provide a substantially improved arrangement for protecting and insulating a tubular support member in a slab reheating furnace or the like.

It is another object of this invention to provide a new tubular support member protecting and insulating arrangement which has a stable structure without requiring mortar.

A further object of this invention is to provide a new tubular support member protecting and insulating arrangement which comprises a layer of resiliently deformable insulating material covered by a layer of interlocking refractory elements, the two layers cooperating with each other in a manner which substantially eliminates paths for gas and heat between the fumace and the surface of the tubular support members, and which minimizes and accommodates stresses `derived from temperature gradients and vibratonal shocks caused by the movement of the slabs through the furnace.

Other objects and the attendant advantages of the present invention Will become apparent from the detailed description to follow together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS There follows a detailed description of preferred embodiments of the present invention to be read together with the accompanying drawings. However, it is to be understood that the detailed description and the accompanying drawings are provided merely for purposes of illustrating preferred embodiments of the invention and that the nvention is capable of numerous modifications and variations apparent to those skilled in the art.

In the drawings:

FIGURE 1 is a schematic drawing of the interior of a slab reheating furnace having tubular support members such as skid rails and support tubes constructed in accordance with the present invention.

FIGURE 2 is an enlarged sectional view taken through a plane perpendicular to the axis of a support tube such as along line A-A or B-B of FIGURE 1.

FIGURE 3 is an enlarged view of a portion of FIG- URE 2.

FIGURE 4 is a view similar to FIGURE 2 but showing an alternate construction of the present invention.

FIGURE 5 is an enlarged view showing a portion of FIGURE 4.

FIGURES 6 and 7 are schematic perspectives illustrating the lower portion of a vertical support tube and illustrating two dilferent arrangements for locating the interlocking elements on the tube.

FIGURE 8 is an enlarged sectional View taken through a plane perpendicular to the axis of a skid rail, such as along line C-C of FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 illustrates, schematically, the environment in which the present invention would be employed. The slab reheating furnace 10 includes skid rails 11 along which slabs 12 are moved in the direction indicated by arrow 13. The slabs are introduced at an inlet opening, not shown, and discharged through a suitable outlet such as opening 14. The skid rails are supported on horizontal Water cooled support tubes -15 which are in turn supported by vertical water cooled support tubes 16, the latter extending from support tubes 15 to pedestals 17. FIGURE 1 also illustrates, schematically, the relative positions of an upper burner 18 and a lower burner 19. It can be seen that the skid rail support tubes stand in the path of the hot gases generated -by the lower burner 19.

FIGURES 2 and 3 illustrate one arrangement of the present invention. The water cooled tube 25 is surrounded by a layer 26 of insulating material, for example, ceramic fiber, which layer is in turn surrounded by a ring or necklace 27 of refractory material. In the embodiment of FIG- URES 2 and 3 the ring 27 is formed by interlocking elements 28, each of which includes a head in the form of an outer flange 31 extending radially inwardly towards the axis of the tube and a tail formed as an inner flange 32 extending radially outwardly away from the axis of the tube. An outer recess 33 is formed adjacent the flange 31 and an inner recess 34 is formed adjacent the inner flange 32. FIGURE 2 illustrates generally and FIGURE 3 illustrates in detail how the individual refractory elements nterlock with each other to form the ring.

Referring to FIGURE 3 it will be noted that a space is provided between the outer flange 31 on the lefthand element and the body of the righthand element 28 and between the inner flange 32 of the righthand element and the body of the lefthand element 28. These spaces permit limited freedom of movement of the elements relative to each other to accommodate thermal stresses and vibratonal shocks created during start up, normal operation and shut down of the slab reheating furnace. At the same time it can be seen that the flanges 31 and 32 are held firmly against each other so that the ring is held in a state of circumferential tension and radially compresses the resiliently deformable layer 26.

FIGURES 4 and 5 illustrate an arrangement similar to FIGURE 2 but employing refractory elements 29 constructed in accordance with another embodiment of the invention. This element 29 is shown in greater detail in FIGURE 5. The refractory elements employed in the embodiment of FIGURES 4 and 5 are not wholly unlike the refractory element shown in British Patent No. 933,- 243. The element 29 includes a projecting head 36 including a forward portion 37 having a relatively small radius of curvature and a rear portion 38 having a larger radius of curvature. The head 36 forms a pair of neck-like recesses 40 between the head 36 and the shoulders 39a and 39b. It will be noted that the shoulders 39a and 39b form a generally straight line slanted backwards towards I the tail of the element from the outside thereof to the inside thereof. This permits the assembly of elements 29 into a ring surrounding a tube. The slope of shoulders 39a and 39b can be varied. In fact, they can both slope outwardly from recess 40 back towards the tail of the element. The main requirement is that they be designed to cooperate with the tail of the element so that the elements can be formed as a ring about a tube. The tail of element 29 is provided in the form of a groove 41 having a radius of curvature slghtly greater than the radius of curvature of the rear head portion 38. This groove 41 is partially closed at lips 42 so that once the head 36 of the adjacent element 29 is placed into the groove 41 (by moving the two elements relative to each other in a direction parallel to the axis of the tube) the two elements cannot be separated by moving one element circumferentially relative to the other. The relieved portion formed by the smaller radius of curvature at forward portion 37 permits movement of the head 36 in the groove 41 to accommodate thermal stresses and vibrational shocks while the elements are held tightly in place on the layer of insulating material 26. It can be seen that the shoulder elements 39a and 39b permit angular deflection of the righthand element 29 relative to the lefthand element 29 so that the chain of elements can be forrned into a ring about the insulating layer 26.

FIGURES 6 and 7 illustrate two possible arrangements for assembling the elements onto a support tube. In FIG- URE 6 the elements are arranged in longitudinally eX- tending rows wherein the elements are staggered relative to the elements in adjacent rows. Normally, in this arrangement, each element will be the same width (for example width D except for end elements in alternate rows which would be of a shorter width (for example D In this manner all of the elements in a given longitudinal row could be shifted to replace a broken element in that row while leaving the remaining rows in place.

FIGURE' 7 illustrates the arrangement wherein all of the elements are the same width (for example width D With this arrangement it is possible to arrange the elements into longitudinally and/or circumferentially eX- tending rows. In FIGURE 7 the elements are arranged in circumferentially extending rows with the elements staggered relative to the elements in adjacent rows. With this arrangement it is possible to replace any given row While leaving the other rows in place.

The arrangements of FIGURES 6 and 7 provide advantages in replacing specific elements or rows of elements as the case may be. The particular arrangement for a given situation would depend upon such factors as the orientation of the support tube, horizontal or vertical, and the relationship of the tube to other tubes.

In carrying out the invention the size of the elements and the size of the refractory layer will depend upon practical design consideratons and, of course, is variable within the spirit and scope of the nvention. However, by way of example, the applicant has found that the following sizes permit a suitable arrangement of the interlocking elements on a water cooled tube.

Inside diameter of assenbly (in inches) No. of segmente Minimum Nomnal Maximum 9 9%` 9% /s` 10% ro /m 1l% ll llV 12 11 12% 12% V 13% 13% 14% 14 14% 15 14% 15 m` 15% 15% 157/ 16% In a suitable embodment of the invention the insulating layer may comprise a ceramic fiber which may be approximately 1 inch in the uncompressed state and a inch when compressed by the refractory layer.

The ceramic fiber layer may be of the type known as Triton manufactured and sold by Morganite Ceramic Fibres, Limited, of England; or it may be of the type known as Kaowool, manufactured by the Babcock and WilcoX Company of the United States. The properties of the ceramic fiber material are explained in detail in the U.S. Patent No. 2,636,723 to Harter et al.

It is convenient to form the refractory elements by conventional extrusion processes, the cross-section of the extrusion die forming the cross-section of the elements as shown in FIGURES 2-5. The elements may then be cut ofi at any convenient length. In a typical embodiment of the invention the elements will be cut into sizes of 3 inches and 6 inches. That is, dimensions D and D may be 6 inches while dimension D might be 3 inches.

The refractory elements may be made of any suitable refractory material. As an example, a suitable refractory material is comprised of 70-80% mullite bonded with a plastic refractory clay (ZO-30%). Mullite is a known refractory made by firing calcined kyanite, a naturally occurring alumina silicate, at about 1450 C.

An example of the application of the invention to a skid rail pipe itself is shown by FIGURE 8 in which a water-cooled metal tube 43 has an integral skid rail rib 44 and is covered by a protecting and insulating arrangement including an inner layer 45 of resiliently deformable heat insulating material resiliently compressed around the tube 43 by an outer layer of segmental refractory elements 46, with interlocking head and tail joints 47, 48, respectively, held in circumerential compression as an arch with the radial faces of adjacent elements thrust into abutment 'at the junction 49 of their end faces by the reaction from resilient compression of the inner layer 45.

The elements 46 ditfer from those shown in FIGURES 4 and 5 primarly by the circumerential curvature of the inner and outer faces. However, it will be noted that the heads and tails of elements 46, like those of FIGURES 4 and 5, are designed to permit limited freedom of movement between adjacent elements. In practice, by using only elements having both heads and tails these elements 46 could be used in the complete circumferential arrangement. Also, the refractory elements shown in FIGURES 4 and 5 could be adapted for use with skid rails by slanting the shoulders 39a and 391), relative to the tail end of the adjacent element, so that a series of interlocked elements will always follow a curved or arcuate path, even when urged outwardly by the resiliently deformable layer as shown in FIGURE 8.

Although the invention has been described in considerable detail with respect to preferred embodiments thereof, it should be apparent that the invention is capable of numerous modifications and Variations apparent to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. In a furnace Construction for use in the heating of steel ingots wherein the steel ingots rest on water cooled tubular support members including skid rails on which they progress through the furnace, and support tubes for supporting the skid rails, whereby coolant can be passed through said tubular support members; an improvement in means for protecting said tubular support members from conditions in the furnace comprising:

an inner layer of heat insulating material disposed immediately over the outer surface of at least one of the said support members and being of a resiliently deformable consistency capable of being partially and resiliently compressed from its thickness in its uncompressed state, and an outer layer of refractory material disposed over the outer surface of said in- &451561 ner layer, the outer layer comprising a plurality of individual elements which interlock with each other circumferentially to form a row, the outer layer being held against the inner layer to cause at least some radial compression of the inner layer, and the said row forming the outer layer being held in a state of circumferential stress by the resiliency of the inner layer.

2. The invention of claim 1 wherein the interlocking elements include means for permitting limited freedom of movement of each element relative to its adjacent elements while retaining the elements in said state of circumferential Stress.

3. The invention of claim 2 wherein the inner and outer layers substantially completely encrcle said support member to form a substantially cylindrically shaped protectng and insulatng arrangement, the elements of said outer layer forming a ring held in 'a state of circumferential tension by the said inner layer.

4. The invention of claim 3 wherein each of said elements includes a head portion and a tail portion, the tail portion being of a shape complementary to the head portion so that adjacent head and tail portions on adjacent elements can be engaged with each other thereby preventing separation of the engaged elements in the circumferential direction, relative to said support member, but permitting flexing of said ring by permitting limited circumferential and pivotal movement of each element relative to its adjacent elements.

5. The invention of claim 3 wherein each of said elements comprises a main body portion, an inner flange and an outer fiange; the inner flange extending outwardly relative to said support member and forming an inner recess between the inner flange and the main body portion; the outer flange extending inwardly towards the support member and forming an outer recess between the outer flange and the main body portion; the width of the inner recess being slightly greater than the width of the outer flange and the width of the outer recess being slightly greater than the width of the inner flange; wherein the inner and outer flanges of each element are positioned within the outer and inner recesses, respectively, of adjacent elements in the formation of the said ring.

6. The invention of claim 3 wherein each of said elements, Viewed in a plane perpendicular to the axis of the support member, includes a main body portion, a circumferentially projecting portion on one side of the body portion and a groove at the other side of said body portion, the said projecting portion including an enlarged head portion and a reduced neck portion, the groove including an enlarged recess of a size slightly greater than the enlarged head portion and a rear opening larger than the thickness of the said reduced neck portion and smaller than the said enlarged head portion.

7. The invention of claim 6 wherein the forward end of the said head portion has a smaller radius of curvature than the rear of the head portion adjacent the neck, and wherein the enlarged recess is generally circular and has a radius of curvature slightly greater than that of the rear of the head portion.

8. The invention of claim 6 wherein the side of the main body portion adjacent the said neck lies in a plane substantially parallel to the support member axis and is slanted, from the outside to the inside of the refractory layer, at an angle toward the said groove of the element.

9. The invention of claim 2 wherein said support member is a generally horizontal water cooled skid rail having formed along the top thereof an upstanding rail rib having an upper surface on which the ingots rest and two longitudinally extending lateral side surfaces, and wherein the said protectng and insulatng arrangement extends circumferentially around and covers the said skid rail between the lateral side surfaces, except for said upper surface of the rib.

10. The invention of claim 9 wherein said outer layer is held in a state of circumferental compression by the said inner layer.

11. The invention of claim 10 wherein each of said elements, viewed in a plane perpendicular to the axis of the support member, includes a main body portion, a circumferentially projecting portion on one side of the body portion and a groove at the other side of said body portion, the said projecting portion including an enlarged head portion and a reduced neck portion, the groove including an enlarged recess of a size slightly greater than the enlarged head portion and a rear opening larger than the thickness of the said reduced neck portion and smaller than the said enlarged head portion.

12. The invention of claim 11 wherein the forward end of the said head portion has a smaller radius of curvature than the rear of the head portion adjacent the neck, and wherein the enlarged recess is generally circular and has a radius of curvature slightly greater than that of the rear of the head portion.

13. The invention of claim 11 wherein the side of the main body portion adjacent the said neck lies in a plane substantially parallel to the support member axis and is slanted, from the outside to the inside of refractory layer, at an angle towards the said groove of the element.

14. The invention of claim 11 wherein the inner and outer surfaces of the refractory layers are curved about an axis corresponding generally to said skid rail axis.

15. The invention of claim 1 wherein the said heat insulating material is ceramic fiber.

16. The invention of claim 1 wherein the elements of the said refractory layer are arranged in rows of aligned elements, each row extending parallel to the axis of the tube.

References Cited UNITED STATES PATENTS 2,884,879 5/ 1959 Corriston. 3,226,101 12/ 1965 Balaz et al.

JOHN J. CAMBY, Primary Exam'ner.

U.S. Cl. X.R. 138 149; 263-44- 

